It was supposed to be released on the great occasion of Christmas but iPhone Dev Team missed the deadline of Christmas to released the untethered jailbreak for the iOS 4.2.1. The untethered jailbreak will have support for Windows and Mac users, I am not sure about the Linux users.
This jailbreak will be in the form of the redsn0w, which would be able to jailbreak all the iDevices including iPod Touch 4G, iPhone and iPad. According to the iPhone Dev Team this jailbreak is not yet ready for the public release, but yes the untethered jailbreak is given to some private testers they will test it and release it for the public very soon.
iPhone Dev Team demoed the untethered jailbreak for iOS 4.2.1 in a form of the video. This jailbreak is more like a backup plan as user’s iOS 42. beta 3 SHSH blobs are stored with Cydia. Comex is also working on an extensible version of the jailbreak, he is finding ways to retain the exploit for the next version of the iOS.
After implementing this jailbreak to your device you may lose the ultrasn0w unlock. To conclude this post I would like to say that userland jailbreak for iOS 42.1 will be out next week and the date for the iOS 4.2.1 is 3rd December 2011. iPhone Dev Team may change the release date of their untethered jailbreak for the iDevices running iOS 4.2.1. Here is a Download Link for Redsn0w 0.9.7 for iOS 4.2.1
via [iPhone Dev Team]